Major emphasis will be given to studies of porphyrin metabolism in tissues of cattle who are homozygous or heterozygous for newly discovered hereditary bovine protoporphyria. Implications of the markedly depressed activity of ferrochelatase in all body tissues studied will be considered with relation to the properties and cellular localization of this enzyme, as well as to its activity relative to that of ALA synthesis and other enzymes involved in porphyrin biosynthesis. Enzyme patterns and porphyrin accumulation in developing normoblasts and reticulocytes will be investigated. Studies of experimental renal porphyria will be continued with special reference to erythropoietin production and other renal functions. Quantitative assays of zinc-bond versus "free" protoporphyrin in red cells and tissues of patients and experimental animals will be continued. BIBLIOGRAPHIC REFERENCES: Schwartz, S., B. Stephenson, D. Sarkar, H. Freyholtz, and W. Runge. Development and implications of experimental renal porphyria: Heme synthetase, ALA dehydratase, and porphyrins in liver, kidney, and Harderian glands of hamsters given DDC, estrogen, and/or cobalt. In Porphyrins in Human Diseases, M. Doss (Ed.), S. Karger, New York, 1976. pp. 370-379. Schwartz, S., P. Edmondson, B. Stephenson, D. Sarkar, and H. Freyholtz. Direct spectrofluorophotometric determination of porphyrin in diluted urine. Ann. Clin. Res. (Helsinki), 8:156-161, 1976.